Trifluoperazine inhibits phagocytosis in a macrophagelike cultured cell line.

Trifluoperazine, a drug that binds to Ca2+-calmodulin and inhibits its interaction with other proteins, was found to inhibit growth and phagocytosis in a macrophagelike cell line, J774.16. Both effects were reversible and occurred at the same concentrations of drug (25--50 microM) that inhibited the activation of cyclic nucleotide phosphodiesterase by calmodulin in vitro. Fc-mediated phagocytosis was also depressed by W-7, a sulfonamide derivative that inhibits the activity of Ca2+-calmodulin. In contrast, taxol, a drug that stabilizes cellular microtubules, had no effect on Fc-mediated phagocytosis although it inhibited cell growth at nanomolar concentrations. The inhibitory effects of trifluoperazine and W-7 on phagocytosis suggest that calmodulin may be involved in this complex cellular function.

Biosynthetic precursors and in vitro translation products of the glucose transporter of human hepatocarcinoma cells, human fibroblasts, and murine preadipocytes.

Antisera to the human erythrocyte Glc transporter immunoblotted a polypeptide of Mr 55,000 in membranes from human hepatocarcinoma cells, Hep G2, human fibroblasts, W138, and murine preadipocytes, 3T3-L1. This antisera immunoprecipitated the erythrocyte protein which had been photoaffinity labeled with [3H]cytochalasin B, immunoblotted its tryptic fragment of Mr 19,000, and immunoblotted the deglycosylated protein as a doublet of Mr 46,000 and 38,000. This doublet reduced to a single polypeptide of Mr 38,000 after boiling. When Hep G2, W138, and 3T3-L1 cells were metabolically labeled with L-[35S]methionine for 6 h, a broad band of Mr 55,000 was immunoprecipitated from membrane extracts. In pulse-chase experiments, two bands of Mr 49,000 and 42,000 were identified as putative precursors of the mature transporter. The t1/2 for mature Glc transporter was 90 min for Hep G2 cells that had been starved for methionine (2 h) and pulsed for 15 min with L-[35S]methionine. Polypeptides of Mr 46,000 and 38,000 were immunoprecipitated from Hep G2 cells that had been metabolically labeled with L-[35S]methionine in the presence of tunicamycin. This doublet reduced to the single polypeptide of Mr 38,000 after boiling. In the absence of tunicamycin, but not in its presence, mature polypeptide of Mr 55,000 was immunoprecipitated from Hep G2 cells metabolically labeled with D-[3H]GlcN. A polypeptide of Mr 38,000 was observed in boiled immune complexes from the in vitro translation products of Hep G2, W138, and 3T3-L1 cell RNA. Dog pancreatic microsomes cotranslationally, but not posttranslationally, converted this to a polypeptide of Mr 35,000. A model for Glc transporter biogenesis is proposed in which the primary translation product of Mr 38,000 is converted by glycosylations to a polypeptide of Mr 42,000. The latter is then processed via heterogeneous complex N-linked glycosylations to form the mature Glc transporter, Mr 55,000.

Glucose deprivation and hexose transporter polypeptides of murine fibroblasts.

The effect of Glc deprivation (starvation) on hexose transporter (GT) polypeptide(s) (pp) was studied in 3T3-C2 murine fibroblasts. Cells deprived of Glc exhibit 5-fold increases in hexose transport and Glc-displaceable cytochalasin B binding. Immunoblots of membranes reveal a Mr 55,000 GT pp in fed (4 g of Glc/liter) cells and Mr 55,000 and Mr 42,000 GT pp in starved cells. A 10-40-fold increase in total GT pp occurs upon Glc deprivation; part of this accumulation (2-5-fold) is in the Mr 55,000 GT pp, and the remaining increase is in the Mr 42,000 GT pp. During the first 12 h of Glc deprivation only the Mr 55,000 GT pp accumulates. At later times (24-72 h) the Mr 42,000 GT pp appears and constitutes a larger fraction of the total accumulation. Similarly, the Glc concentration dependence of these phenomena reveals that the Mr 55,000 GT pp accumulates at higher concentrations of Glc (less than or equal to g/liter) than the Mr 42,000 GT pp (less than or equal to 0.5 g/liter). Using alternative nutrients, sugar analogs, and inhibitors we observed that the accumulation of total GT pp is dependent upon both hexose phosphate metabolism and the interaction of substrate with the GT. The role(s) of oligosaccharide biosynthesis, protein synthesis, and the transport process itself in the Glc deprivation-induced accumulation of GT pp were examined. The appearance of the Mr 42,000 GT pp but not the Mr 55,000 GT pp was dependent upon protein synthesis. The Glc deprivation-induced accumulation of GT pp is reversible upon refeeding with Glc (4 g/liter, 12 h). This reversal was dependent upon protein synthesis. The electrophoretic mobility of the Mr 42,000 GT pp is similar to the GT pp observed after tunicamycin treatment. The Mr 55,000 but not the Mr 42,000 GT pp binds specifically to agarose-bound wheat germ agglutinin and is sensitive to endoglycosidase F digestion. Oligosaccharide-stripped GT pp and the Mr 42,000 GT pp have the same Mr. The results suggest that the accumulation of total GT pp induced by Glc deprivation is partially independent of the effect of Glc deprivation on glycoprotein biogenesis. The appearance of the Mr 42,000 GT pp with aglyco characteristics is the result of the latter. The accumulation of total GT pp, however, is the result of a specialized and sensitive adaptation of the cell to Glc deprivation. The GT pp synthesized during chronic Glc deprivation has an Mr of 42,000; fed cells synthesize the Mr 55,000 GT pp. Neither the level of in vitro translatable GT mRNA nor the rate of GT pp synthesis are increased by Glc deprivation.(ABSTRACT TRUNCATED AT 400 WORDS)